About this Chapter

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

About this Chapter

Fluid and electrolyte homeostasis

Water balance

Sodium balance and ECF volume

Potassium balance

Behavioral mechanism in salt and water balance

Integrated control of volume and osmolarity

Acid-base balance


Fluid and Electrolyte Homeostasis

Na+ and water: ECF volume and osmolarity

K+: cardiac and muscle function

Ca2+: exocytosis, muscle contractions, and other functions

H+ and HCO3–: pH balance

Body must maintain mass balance Excretion routes: kidney and lungs



The body’s integrated response to changes in blood volume and blood pressure

Figure 20-1a

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 20-2

Water Balance in the Body


Water Balance

A model of the role of the kidneys in water balance


Urine Concentration

Osmolarity changes as filtrate flows through the nephron

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 20-5a

Water Reabsorption

Water movement in the collecting duct in the presence and absence of vasopressin

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 20-5b

Water Reabsorption


Water Reabsorption

The mechanism of vasopressin action

Collecting duct lumen

Filtrate300 mOsm

H2O

Exocytosisof vesicles

Cross-section ofkidney tubule

Collecting duct cell

Secondmessengersignal

H2O

cAMP

Storage vesicles

Aquaporin-2water pores

600 mOsM

H2O

Medullaryinterstitial

fluid

Vasopressin receptor

600 mOsM

Vasarecta

H2O

700 mOsM

Vasopressin

Vasopressin binds to mem-brane receptor.

Receptor activates cAMP second messenger system.

Cell inserts AQP2 water pores into apical membrane.

Water is absorbed by osmosis into the blood.

1 2 3 4

1

2

3

4

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 20-6, step 1

Water Reabsorption


Filtrate300 mOsm


Collecting duct cellMedullaryinterstitial

fluid


Vasarecta

Vasopressin


1

1

600 mOsM

600 mOsM

700 mOsM

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 20-6, steps 1–2

Water Reabsorption


Filtrate300 mOsm




cAMP


fluid


Vasarecta

Vasopressin



1 2

1

2

600 mOsM

600 mOsM

700 mOsM


Water Reabsorption


Filtrate300 mOsm





cAMP

Storage vesicles



fluid


Vasarecta

Vasopressin




1 2 3

1

2

3

600 mOsM

600 mOsM

700 mOsM


Water Reabsorption


Filtrate300 mOsm

H2O





H2O

cAMP

Storage vesicles


600 mOsM

H2O


fluid


600 mOsM

Vasarecta

H2O

700 mOsM

Vasopressin




Water is absorbed by osmosis into the blood.

1 2 3 4

1

2

3

4


Factors Affecting Vasopressin Release


Water Balance

The effect of plasma osmolarity on vasopressin secretion by the posterior pituitary


Countercurrent Heat Exchanger


Water Balance

Countercurrent exchange in the medulla of the kidney


Ion reabsorption

Active reabsorption of ions in the thick ascending limb creates a dilute filtrate in the lumen


Fluid and Electrolyte Balance

Vasa recta removes water Close anatomical association of the loop of Henle and

the vasa recta

Urea increase the osmolarity of the medullary interstitium


Animation: Urinary System: Late Filtrate ProcessingPLAY

Sodium Balance

Homeostatic responses to salt ingestion


Sodium Balance

Aldosterone action in principle cells

Interstitialfluid

Blood

Aldosterone

ATP

Aldosteronereceptor

Newchannels

P cell of distal nephron

Translation andprotein synthesis

Proteins modulateexisting channels and pumps.

New pumps

K+

Na+

K+ K+

Na+

Na+

ATP

K+

secreted

Na+

reabsorbed

Lumen of distal

tubule

Aldosterone combines with a cytoplasmic receptor.

Hormone-receptor complex initiates transcription in the nucleus.

New protein channelsand pumps are made.

Aldosterone-induced proteins modify existing proteins.

Result is increased Na+ reabsorptionand K+ secretion.

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3

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Transcription

mRNA


Sodium Balance

Interstitialfluid

Blood

Aldosterone

Aldosteronereceptor


Lumen of distal

tubule


1

1


Sodium Balance

Interstitialfluid

Blood

Aldosterone

Aldosteronereceptor


Lumen of distal

tubule



1

2

12Transcription

mRNA


Sodium Balance

Interstitialfluid

Blood

Aldosterone

ATP

Aldosteronereceptor



Lumen of distal

tubule




1

2

3

12

3

Transcription

mRNA

Newchannels New pumps


Sodium Balance

Interstitialfluid

Blood

Aldosterone

ATP

Aldosteronereceptor



ATP

Lumen of distal

tubule





1

2

3

4

12

3

4

Transcription

mRNA

Newchannels


New pumps


Sodium Balance

Interstitialfluid

Blood

Aldosterone

ATP

Aldosteronereceptor



K+

Na+

K+ K+

Na+

Na+

ATP

K+

secreted

Na+

reabsorbed

Lumen of distal

tubule





Result is increased Na+ reabsorptionand K+ secretion.

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3

4

5

Transcription

mRNA

Newchannels


New pumps


Sodium Balance

The renin-angiotensin-aldosterone pathway


Sodium Balance

Decreased blood pressure stimulates renin secretion


Sodium Balance

Action of natriuretic peptides


Potassium Balance

Regulatory mechanisms keep plasma potassium in narrow range Aldosterone plays a critical role

Hypokalemia Muscle weakness and failure of respiratory muscles

and the heart

Hyperkalemia Can lead to cardiac arrhythmias

Causes include kidney disease, diarrhea, and diuretics


Behavioral Mechanisms

Drinking replaces fluid loss

Low sodium stimulates salt appetite

Avoidance behaviors help prevent dehydration Desert animals avoid the heat


Disturbances in Volume and Osmolarity

Animation: Fluid, Electrolyte, and Acid/Base Balance: Water HomeostasisPLAY

Figure 20-17


Volume and Osmolarity


Blood volume/ Blood pressure

Osmolarity

Granularcells

GFRFlow atmacula densa

accompanied by

CVCC

Parasympatheticoutput

Sympatheticoutput

Heart

ForceRate

Cardiacoutput

Vasoconstriction

Peripheralresistance

Angiotensinogen ANG I

ACE

ANG II

Aldosterone

Na+

reabsorption

Distalnephron Distal

nephron

Vasopressin release from

posterior pituitary

Arterioles

VolumeH2O

reabsorption

H2O intake

Thirst

Volumeconserved

Hypothalamus

Adrenalcortex

DEHYDRATION

CARDIOVASCULARMECHANISMS

RENIN-ANGIOTENSINSYSTEM

RENALMECHANISMS

HYPOTHALAMICMECHANISMS

Carotid and aorticbaroreceptors

Hypothalamicosmoreceptors

Atrial volume receptors; carotid

and aorticbaroreceptors

Osmolarity

Bloodpressure

+

++

+

++

+

+

+

+

+

Renin

osmolarity inhibits

Figure 20-18


Homeostatic compensation for severe dehydration

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 20-18 (1 of 6)



CVCC


Sympatheticoutput

Heart

ForceRate

Cardiacoutput

Vasoconstriction


Arterioles

DEHYDRATION



Bloodpressure




Osmolarityaccompanied by

Distalnephron


posterior pituitary

VolumeH2O

reabsorption

H2O intake

Thirst

Hypothalamus

DEHYDRATION

HYPOTHALAMICMECHANISMS Hypothalamic

osmoreceptors



Osmolarity

Bloodpressure

+

+




Granularcells



ACE

ANG II

Volumeconserved

DEHYDRATION


RENALMECHANISMS

+

+

Renin




Osmolarity

Granularcells

accompanied by

CVCC


ACE

ANG II

Aldosterone

Na+

reabsorption

Distalnephron


posterior pituitary

Arterioles Thirst

Adrenalcortex

DEHYDRATION


+

+

+ ++

+

Renin

osmolarity inhibits




Osmolarity

Granularcells


accompanied by

CVCC


Sympatheticoutput

Vasoconstriction


ACE

ANG II

Aldosterone

Na+

reabsorption


nephron


posterior pituitary

Arterioles

VolumeH2O

reabsorption

H2O intake

Thirst

Volumeconserved

Adrenalcortex

DEHYDRATION


RENALMECHANISMS

Osmolarity

Bloodpressure

+

++

+

+ +

+

+

+

Renin

osmolarity inhibits




Osmolarity

Granularcells


accompanied by

CVCC


Sympatheticoutput

Heart

ForceRate

Cardiacoutput

Vasoconstriction



ACE

ANG II

Aldosterone

Na+

reabsorption


nephron


posterior pituitary

Arterioles

VolumeH2O

reabsorption

H2O intake

Thirst

Volumeconserved

Hypothalamus

Adrenalcortex

DEHYDRATION



RENALMECHANISMS

HYPOTHALAMICMECHANISMS


Hypothalamicosmoreceptors



Osmolarity

Bloodpressure

+

++

+

++

+

+

+

+

+

Renin

osmolarity inhibits


Acid-Base Balance

Normal pH of plasma is 7.38–7.42

H+ concentration is closely regulated Changes can alter tertiary structure of proteins

Abnormal pH affects the nervous system Acidosis: neurons become less excitable and CNS

depression

Alkalosis: hyperexcitable

pH disturbances Associated with K+ disturbances


Acid-Base Balance

Hydrogen balance in the body


Acid and Base InputAcid Organic acids

Diet and intermediates Under extraordinary conditions

Metabolic organic acid production can increase Ketoacids

Diabetes Production of CO2

Acid production

Base Few dietary sources of bases


pH Homeostasis

Buffers moderate changes in pH Cellular proteins, phosphate ions, and hemoglobin

Ventilation Rapid

75% of disturbances

Renal regulation Directly excreting or reabsorbing H+

Indirectly by change in the rate at which HCO3– buffer

is reabsorbed or excreted


pH Disturbances

The reflex pathway for respiratory compensation of metabolic acidosis


pH Disturbances

Overview of renal compensation for acidosis


Renal Compensation: Transporters

Apical Na+-H+ antiport

Basolateral Na+-HCO3– symport

H+-ATPase

H+-K+-ATPase

Na+-NH4+ antiport


Renal Compensation

Proximal tubule H+ secretion and the reabsorption of filtered HCO3

–

Peritubularcapillary

Interstitialfluid

Reabsorbed

Filtration

Proximal tubule cell

Glomerulus

HCO3–

H+ + HCO3–

HCO3–

CO2+

H2O

H+ Na+ Na+

Secreted H+

Na+

HCO3–

Na+

Bowman’scapsule

H2O + CO2

Filtered HCO3– + H+

Secreted H+ and NH4+

will be excreted

Na+

Na+

KG HCO3–

Na+

NH4+ HCO3

–

Na+

Glutamine

CA

Na+-H+ antiport secretes H+.

H+ in filtrate combines with filtered HCO3

– to form CO2.

CO2 diffuses into cell and combines with water to form H+ and HCO3

–.

H+ is secreted again and excreted.

HCO3– is

reabsorbed.

Glutamine is metabolized to ammonium ion and HCO3

–.

NH4+ is secreted

and excreted.

HCO3– is reabsorbed.

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2

4

3

6

7

5

8


Renal Compensation


Interstitialfluid

Filtration


Glomerulus

H+ Na+ Na+

Secreted H+

Bowman’scapsule

Na+


1

1


Renal Compensation


Interstitialfluid

Filtration


Glomerulus

HCO3–

H+ Na+ Na+

Secreted H+

Bowman’scapsule

H2O + CO2


Na+



– to form CO2.

1

2

1

2


Renal Compensation


Interstitialfluid

Filtration


Glomerulus

HCO3–

H+ + HCO3–

CO2+

H2O

H+ Na+ Na+

Secreted H+

Bowman’scapsule

H2O + CO2


Na+



– to form CO2.


–.

1

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1

2

3

CA


Renal Compensation


Interstitialfluid

Filtration


Glomerulus

HCO3–

H+ + HCO3–

CO2+

H2O

H+ Na+ Na+

Secreted H+

Bowman’scapsule

H2O + CO2


Secreted H+

will be excreted

Na+



– to form CO2.


–.


1

2

4

3

1

2

4

3

CA


Renal Compensation


Interstitialfluid

Reabsorbed

Filtration


Glomerulus

HCO3–

H+ + HCO3–

HCO3–

CO2+

H2O

H+ Na+ Na+

Secreted H+

Na+

HCO3–

Na+

Bowman’scapsule

H2O + CO2


Secreted H+

will be excreted

Na+



– to form CO2.


–.


HCO3– is

reabsorbed.

1

2

4

3

5

1

2

4

3

5

CA


Renal Compensation


Interstitialfluid

Reabsorbed

Filtration


Glomerulus

HCO3–

H+ + HCO3–

HCO3–

CO2+

H2O

H+ Na+ Na+

Secreted H+

Na+

HCO3–

Na+

Bowman’scapsule

H2O + CO2


Secreted H+

will be excreted

Na+

KG HCO3–NH4

+

Glutamine



– to form CO2.


–.


HCO3– is

reabsorbed.


–.

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2

4

3

6

5

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2

4

3

6

5

CA


Renal Compensation


Interstitialfluid

Reabsorbed

Filtration


Glomerulus

HCO3–

H+ + HCO3–

HCO3–

CO2+

H2O

H+ Na+ Na+

Secreted H+

Na+

HCO3–

Na+

Bowman’scapsule

H2O + CO2



will be excreted

Na+

Na+

KG HCO3–NH4

+

Glutamine



– to form CO2.


–.


HCO3– is

reabsorbed.


–.

NH4+ is secreted

and excreted.

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2

4

3

6

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5

1

2

4

3

6

7

5

CA


Renal Compensation


Interstitialfluid

Reabsorbed

Filtration


Glomerulus

HCO3–

H+ + HCO3–

HCO3–

CO2+

H2O

H+ Na+ Na+

Secreted H+

Na+

HCO3–

Na+

Bowman’scapsule

H2O + CO2



will be excreted

Na+

Na+

KG HCO3–

Na+

NH4+ HCO3

–

Na+

Glutamine



– to form CO2.


–.


HCO3– is

reabsorbed.


–.

NH4+ is secreted

and excreted.

HCO3– is reabsorbed.

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3

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2

4

3

6

7

5

8

CA


Intercalated Cells

Role of intercalated cells in acidosis and alkalosis


Acid-Base Balance

Animation: Fluid, Electrolyte, and Acid/Base Balance:Acid/Base HomeostasisPLAY


Summary

Fluid and electrolyte homeostasis

Water balance Vasopressin, aquaporin, osmoreceptors,

countercurrent multiplier, and vasa recta

Sodium balance Aldosterone, principal cells, ANG I and II, renin,

angiotensinogen, ACE, and ANP

Potassium balance Hyperkalemia and hypokalemia


Summary

Behavioral mechanisms

Integrated control of volume and osmolarity

Acid-base balance Buffers, ventilation, and kidney

Acidosis and alkalosis

Intercalated cells

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